1. Field of the Invention
This invention relates to a vehicle steering control system and a method of operating the same system, and more particularly to an improvement in the vehicle steering control system capable of turning vehicle rear wheels in the same or opposite direction relative to vehicle front wheels and the operating the same system for the purpose of attaining high vehicle cornering performance.
2. Description of Prior Art
In order to improve cornering performance of modern automotive vehicles, a vehicle steering control system in which both front and rear wheels are steerable or turnable has been proposed which is disclosed, for example, as "a compliance steer control system" in U.S. Pat. No. 4,440,254 issued on Apr. 3, 1984 in the name of Shibahata et al.
This compliance steer control system is composed of hydraulic actuators incorporated with elastomeric insulators interposed between a rear suspension member and a vehicle body. The hydraulic actuators are controllably actuated by hydraulic fluid being supplied to a power cylinder of a power steering system for the front wheels. As a result, the rear wheels are turned in the same or opposite direction relative to the turning of the front wheels. This accomplishes a control to decrease or increase so-called compliance steer of the rear wheels caused during vehicle cornering.
Furthermore, in order to improve vehicle cruising stability and cornering performance the compliance steer control system has been employed to provide a change-over in turning directions of the rear wheels, i.e., the same or opposite turning direction relative to the turning direction of the front wheels, in response to vehicle speed. However, drawbacks have been encountered in the above mentioned compliance steer control system when the hydraulic actuators for the rear wheels continue receiving a certain amount of hydraulic fluid when the change-over operation takes place. This excessive supplied fluid may cause shock during the change-over operation.